Approval and praise within part of theatre (7)
I believe the answer is:
plaudit
'approval' is the definition.
(I know that plaudit is a type of approval)
'praise within part of theatre' is the wordplay.
'praise' becomes 'laud' (lauding is a kind of praising).
'within' means one lot of letters goes inside another.
'part of theatre' becomes 'pit' ('pit' is part of 'theatre').
'laud' going within 'pit' is 'PLAUDIT'.
'and' acts as a link.
(Other definitions for plaudit that I've seen before include "Cheer" , "Salute" , "Commendation, acclamation" , "Acclaim" , "Expression of praise or approval" .)